Buying a Pulse Oximeter

Discussion created by Thomas3.20.2010 on Apr 26, 2017
Latest reply on Apr 27, 2017 by Giulia

First, let's talk about what a pulse/ox is.

A pulse oximeter is a simple non-invasive device that tells you how fast your pulse is and how much of the hemoglobin in blood is carrying oxygen (oxygen saturation).

You can imagine hemoglobin molecules( Hb) as “cars” and the “roads” being our blood vessels. The oxygen molecules get into these cars and travel around the body till they reach their destination. Oxygen saturation tells you the percentage of the total hemoglobin that is carrying oxygen.

When you put your finger into a pulse/ox 2 kinds of light pass through your finger and are detected on the opposite side of the device.

Hemoglobin (Hb) absorbs light. This property is described in a law in physics called “Beer’s Law”.

Beer’s Law: Amount of light absorbed is proportional to the concentration of the light absorbing substance.

By measuring how much light reaches the light detector, the pulse oximeter knows how much light has been absorbed. The more Hb in the finger , the more light is absorbed.

The amount of light absorbed is proportional to the length of the light path. The light emitted from the source has to travel through the artery. The light travels in a shorter path in the narrow artery and travels through a longer path in the wider artery. But arteries pulsate and the device has to measure this pulse in order to calculate oxygen saturation.

Oxygen rich hemoglobin (full cars) and deoxy hemoglobin (empty cars) absorb light of different wavelengths in a specific way. Different “colors” of light have their own wavelength. A pulse/ox uses a special light source which can adjust the wavelength of the light it emits. This light source sequentially passes light of 2 different wavelengths (red light and infrared light) through a sample of oxy Hb. The detector notes how much light, at each wavelength, has been absorbed.

Oxy Hb absorbs more infrared light than red light while deoxy Hb absorbs more Red light than Infrared light. The pulse oximeter works out the oxygen saturation by comparing how much red light and infra red light is absorbed by the blood.

For example, when you have an oxygen saturation of 75 % the blood has both , oxy Hb and deoxy Hb (empty and full cars). The ratio of absorbed red light and infrared light is different and using this information, the pulse oximeter is able to calculate the oxygen saturation as 75 %.

So why would I want to own a pulse/ox?


  • Easy to use and affordable
  • Beneficial for monitoring a wide variety of chronic illnesses, including COPD, asthma and other chronic health conditions
  • Non-invasive, pain-free and convenient
  • Can be used continuously, which is beneficial for monitoring patients who desaturate at night, during sleep
  • Allows for the accurate use of oxygen.
  • Provides the user, or their caregiver, with early warning of impending or existing hypoxemia (low blood oxygen)
  • Provides oxygen saturation trends during physical activity allowing patients, under the advice of their doctors, to easily adjust oxygen to meet their individual needs


Healthy individuals typically register readings above 97%. A healthy body should never fall below 95%, although oxygen saturation above 92% is generally considered safe.  My guideline is 90% - any lower and I immediately seek medical care. I have seen folks in their 60s! Don't go there, folks! Low 80s means call an ambulance now!

So how do I decide which pulse/ox to buy?

I'm not here to sell devices! Whatever device you select please take it to your Doctor's appointment with you and check your Oxygen Sats right after they have - see if you get the same number. Accuracy is very important!

Before purchasing a home pulse oximeter, you should understand the following:

  • They may provide a false reading. For example, a COPD patient can be severely short of breath, but their oxygen saturation reading may be normal.
  • They may be ineffective in the presence of certain conditions. Even wearing black, green or blue nail polish can affect the readings.
  • They may lag behind a patient's condition. For example, the blood oxygen level (PaO2) could potentially decrease to a critical level before the decreased SpO2 (oxygen saturation reading) is displayed on the monitor.

Although widely accepted in clinical and home settings, pulse oximetry should never replace blood gas analysis and/or sound medical advice from your doctor. It should only be used as a screening tool when low blood oxygen levels are suspected.

If you don't have one, go get one and if you have one, take it with you everywhere and use it frequently. It will help you take care of you!